In the plastics industry it is known to mix or blend a moldable base resin with various well-known materials or additives such as powders, fibrous materials, or pellets to provide a blend of material which has the proper proportion of additive and resin for a subsequent molding. The additives are for various purposes with respect to a molded article such as dry coloring powders for color purposes, filaments of fiberglass for strength purposes, powdered or pelletized additives for providing low cost fillers or for improved appearance or strength. All of such additives are well known and are commonly transported to a mixing chamber of a blender by being entrained in an air conveying system usually a vacuum system. Such mixing chambers are normally vertically extending members having a lower discharge opening in communication with the material inlet of a molding machine. Although such mixing chambers may be of any suitable configuration, such chambers are most frequently an inverted truncated conical member to permit a rotary mixing blade to rotate therein inwardly and uniformly adjacent the inner surface of the chamber.
In view of the various characteristics of the materials to be blended or mixed, prior blender chambers have utilized a series of circumferentially spaced break up bars which extend rigidly and vertically along the inner surface of the mixing chamber to prevent the materials being blended from becoming radially stratified. Prior break up bars of 1/8 inch thickness and 1/2 inch width spaced every 60 or 90 degrees have been commonly used. Such break up bars also prevent material from uninterrupted circulation around the inner periphery of the mixing chamber. Such break up bars are normally satisfactory for mixing molding additives and resins; however, there are various materials whereby break up bars do not provide uniform blending. In the instance of dry powders, and in particular dry color powders which frequently are quite fine, the fineness of the powder requires a low mixing blade speed, such as 150 rpm and lower, to prevent the powder from escaping as a dust. Under such conditions the dry powders will build up on the trailing surface or ledge of the break up bars, that is, the 1/8 inch dimension of the illustrative dimensions. Such build up of powders is erratic and inconsistent and at random times one or more of the accumulations of dry powder will break away from the break up bar or bars and enter the material being blended such that the blend will have a higher percentage of colorant with a resultant variation in product color. In many instances color consistency of a molded product is very important; however, in instances where consistent color is not essential, such as on molded plastic cutlery, color consistency will help sell the product. It will also be realized that as the dry color builds up the blend will be color starved which also produces a color variation in the molded products.
Another particular problem with such break up bars occurs with sticky additives--frequently fillers. Such sticky materials stick to the sidewall of the mixer between the break up bars until an agglomeration of the accumulated material breaks off from the sidewall and enters the blend material. Such sticky agglomerations can cause the mixer chamber discharge opening to become clogged or blocked or undesirable molded products. Obviously in a mixer with breaker bars the rotating mixer blade must clear the break up bars.
Prior blenders did not provide for any means below the mixing chamber; that is upwardly adjacent the inlet of the molding machine, for preventing hang-up or bridging of blended material in the discharge throat below the blender chamber. The present structure provides a pivoting blade which breaks up material in the discharge throat and facilitates the removal of the mixing chamber from the molding machine for cleaning purposes.
An illustration of a prior compounding blender is shown in Engineering Data No. 108 (copy attached) and Engineering data No. 115 distributed by Conair, Inc. of Franklin, Pa. The break up bars on the inner conical surface of the mixing or blending chamber are not shown in such publication.